Monstrillopsis planifrons sp. n., adult female holotype from the Canadian Arctic. A right antennule showing armature following nomenclature by Grygier & Ohtsuka (1995), dorsal view B cephalic area showing forehead and perioral ornamentation, lateral view C cephalic area, showing cuticular processes and ornamentation, ventral view, arrow shows supernumerary spiniform element on first segment of left antennule D detail of first and second antennulary segments of left antennule showing supernumerary spiniform element on first segment (*) E fifth leg, ventral view showing small lobe-like processes on inner margin of exopodal (outer) lobes (arrowed) F urosome, showing fifth legs and ovigerous spines, lateral view. Scale bars: A 200 µm, B–F 100 µm, D–E 50 µm.